Surface Area Silicon Research Articles

Mpact of laser surface modification on polycrystalline silicon photovoltaic cell by means of CO2 laser

In this research, we investigate the effect of laser texturing on the photo-electrical properties of the polycrystalline silicon solar cell. Laser surface texturing technique was used to achieve the texturing results, which based on the interaction between pulsed CO2 laser (10.6μm) and polycrystalline silicon used for solar cells. Four of photovoltaic solar cells have been textured in two dimensions in different ranges (1 cm x 1cm and 2 cm x 2 cm) with different line spacing. Solar cells with laser-modified surface were characterized by SEM as well as photo-electrically before and after texturing process. The obtained results showed that laser surface texturing with small grooves spacing, results in increasing of the melted silicon surface area which enhance the silicon electrical properties. Furthermore, it increases the optical path length inside the solar cell which enhances light trapping.

The Influence of Wire Speed on Phase Transitions and Residual Stress in Single Crystal Silicon Wafers Sawn by Resin Bonded Diamond Wire Saw.

Lower warp is required for the single crystal silicon wafers sawn by a fixed diamond wire saw with the thinness of a silicon wafer. The residual stress in the surface layer of the silicon wafer is the primary reason for warp, which is generated by the phase transitions, elastic-plastic deformation, and non-uniform distribution of thermal energy during wire sawing. In this paper, an experiment of multi-wire sawing single crystal silicon is carried out, and the Raman spectra technique is used to detect the phase transitions and residual stress in the surface layer of the silicon wafers. Three different wire speeds are used to study the effect of wire speed on phase transition and residual stress of the silicon wafers. The experimental results indicate that amorphous silicon is generated during resin bonded diamond wire sawing, of which the Raman peaks are at 178.9 cm−1 and 468.5 cm−1. The ratio of the amorphous silicon surface area and the surface area of a single crystal silicon, and the depth of amorphous silicon layer increases with the increasing of wire speed. This indicates that more amorphous silicon is generated. There is both compressive stress and tensile stress on the surface layer of the silicon wafer. The residual tensile stress is between 0 and 200 MPa, and the compressive stress is between 0 and 300 MPa for the experimental results of this paper. Moreover, the residual stress increases with the increase of wire speed, indicating more amorphous silicon generated as well.

The Influence of Stream Treatment on the Activity of Iron-Pillared Montmorillonite in Vacuum Gas Oil Cracking

This study considers the influence of stream treatment on the activity if iron-pillared montmorillonite in vacuum gas oil cracking and the change in its physical-chemical characteristics. Stream treatment was demonstrated to result in a decreased specific surface area and iron and silicon content, as well as in the strengthening of the catalysts. After stream treatment, gasoline and gas yield is reduced and raw material conversion decreases. Before stream treatment, the proportion of aromatic hydrocarbons in cracking gasoline does not exceed 24.1%, while the isoparaffin content is 24,5%. After stream treatment, the aromatization of gasoline increases and the content of paraffin-naphthenic hydrocarbons decreases. The main component of cracking gases is butane-butylene fraction with a content equal to about 40% before stream treatment, which remains unchanged after processing.

Exploring Different Synthesis Parameters for the Preparation of Metal-Nitrogen-Carbon Type Oxygen Reduction Catalysts

The influence of various synthesis conditions of a metal-nitrogen-carbon (M-N/C) catalyst material on oxygen reduction reaction (ORR) kinetics is discussed. Seven M-N/C catalysts based on cobalt are obtained by changing various synthesis conditions, such as the mixing environment, pyrolysis gas, and post-treatment. The ORR activity and stability measurements are performed using the classical three-electrode configuration in a 0.1 M HClO4 solution. The most active and stable ORR catalyst proves to be the material obtained by mixing a cobalt salt, 2,2’-bipyridine, and a high surface area silicon carbide derived carbon together in water and pyrolyzing the mixture in argon. In a fuel cell test, however, a maximum power density value of 135 mW cm−2 is achieved with the catalyst mixed together in a planetary ball-mill at a low catalyst loading of 1.0 ± 0.1 mg cm−2 and at a test cell temperature of 60 oC despite of the fact that preparing the catalyst via dry ball-milling reduces the surface area of the material roughly 40% more than in the case of using a solution-based method. Consequently, mixing the catalyst precursors together without any additional chemicals in a planetary ball-mill instead of in a solution appears to be the most promising choice.

A Fully Flexible Circuit Implementation of Clique-Based Neural Networks in 65-nm CMOS

Clique-based neural networks implement low-complexity functions working with a reduced connectivity between neurons. Thus, they address very specific applications operating with a very low-energy budget. However, the implementation in the state of the art is not flexible and a fabricated circuit is only usable in a unique use case. Besides, the silicon area of hardwired circuits grows exponentially with the number of implemented neurons that is prohibitive for embedded applications. This paper proposes a flexible and iterative neural architecture capable of implementing multiple types of clique-based neural networks of up to 3968 neurons. The circuit has been integrated in an ST 65-nm CMOS ASIC and occupies a 0.21-mm2 silicon surface area. The proper functioning of the circuit is illustrated using two application cases: a keyword recovery application and an electrocardiogram classification. The neurons outputs are updated 83 ns after a stimulation, and a neuron needs an energy of 115 fJ to propagate a change at the input to its output.

Performance evaluation of a curved electrode actuator fabricated without gold/chromium conductive layers

Curved electrode actuators displace on the order of a biological cell diameter at low actuation voltages, making them a potential candidate for probing and micromanipulation of cells in an underwater, closed microenvironment. Here, a closed microenvironment is formed by bonding a Polydimethylsiloxane-based cap-like structure to the actuator; however, the presence of Au/Cr conductive layers on the actuator reduce the available silicon surface area of the actuator—resulting in poor adhesion. Therefore, we propose to fabricate the actuators without these conductive layers. In this paper, we demonstrate the absence of these layers has a minimal effect on the actuator’s peak-to-peak displacement and force. The actuator achieves the following performance metrics: large displacement (1–10 μm) and force (1–21.5 μN) range; broad frequency range (1–500 Hz); and low actuation voltages (0–8 V) in viscous media that are necessary for cell probing and micromanipulation applications.

Neural electrode resilience against dielectric damage may be improved by use of highly doped silicon as a conductive material

BackgroundDielectric damage occurring in vivo to neural electrodes, leading to conductive material exposure and impedance reduction over time, limits the functional lifetime and clinical viability of neuroprosthetics. We used silicon micromachined Utah Electrode Arrays (UEAs) with iridium oxide (IrOx) tip metallization and parylene C dielectric encapsulation to understand the factors affecting device resilience and drive improvements. New methodIn vitro impedance measurements and finite element analyses were conducted to evaluate how exposed surface area of silicon and IrOx affect UEA properties. Through an aggressive in vitro reactive accelerated aging (RAA) protocol, in vivo parylene degradation was simulated on UEAs to explore agreement with our models. Electrochemical properties of silicon and other common electrode materials were compared to help inform material choice in future neural electrode designs. ResultsExposure of silicon on UEAs was found to primarily affect impedance at frequencies >1kHz, while characteristics at 1 kHz and below were largely unchanged. Post-RAA impedance reduction of UEAs was mitigated in cases where dielectric damage was more likely to expose silicon instead of IrOx. Silicon was found to have a per-area electrochemical impedance >10×higher than many common electrode materials regardless of doping level and resistivity, making it best suited for use as a low-shunting conductor. Comparison with existing methodsNon-semiconductor electrode materials commonly used in neural electrode design are more susceptible to shunting neural interface signals through dielectric defects, compared to highly doped silicon. ConclusionStrategic use of silicon and similar materials may increase neural electrode robustness against encapsulation failures.

Mechanisms of high-regularity periodic structuring of silicon surface by sub-MHz repetition rate ultrashort laser pulses

Silicon is one of the most abundant materials which is used in many areas of modern research and technology. A variety of those applications require surface nanopatterning with minimum structure defects. However, the high-quality nanostructuring of large areas of silicon surface at industrially acceptable speed is still a challenge. Here, we report a rapid formation of highly regular laser-induced periodic surface structures (HR-LIPSS) in the regime of strong ablation by infrared femtosecond laser pulses at sub-MHz repetition rate. Parameters of the laser-surface interactions and obtained experimental results suggest an important role of electrostatically assisted bond softening in initiating the HR-LIPSS formation.

Integrated All Solid Micro-Supercapacitors Based on Bottom-up Silicon Nanostructures: From Nanomaterials to Cutting-Edge on-Chip Devices

Over the last two decades, Electrochemical Double Layer Capacitors (or EDLCs) attracted considerable attention since they bridge the gap between batteries and conventional capacitors by combining high energy and power density with an unmatched stability1. Moreover, the relative ease of miniaturization of EDLCs opens a wide horizon of applications such as autonomous sensor networks, active RFID…2 Although carbon is the most studied electrode material for micro-EDLCs, silicon remains the material of choice for “on-chip” integration, provided its surface area is sufficient to allow high capacitance values. Among the various strategies to design high surface area silicon nanostructures, the bottom-up CVD approach permits a fine tuning of the electrical and morphological parameters of the nanostructuresin order to obtain the highest values of capacitance, energy and power densities, while retaining high electrode conductivity and electrochemical robustness. EDLCs based on highly doped CVD silicon nanowires (Si-NWs)3 and nanotrees (Si-NTrs)4 were recently designed and proved extremely beneficial in terms of electrochemical window (4 V)5, maximal power densities (225 mW.cm-2) and cyclability (>106 charge/discharge cycles). Adding branches to Si-NWs to yield Si-NTrs also largely improved capacitance values, proving the versatility and potentiality of the bottom-up approach. However, previously published work rarely studied the influence of the morphological parameters on the supercapacitive behavior of the SiNTr-based electrodes and several steps are still required to permit “on chip” integration. In the present work, we improved previously published performances by designing advanced Si-NTrs morphologies using a simple, selective and cost effective electroless gold deposition method for the CVD catalyst deposition steps. The highly conductive Si-NTrs forests were optimized concerning “trunks” and “branches” density, length and diameters, yielding a single electrode specific capacitance value as high as 1.7 mF.cm-2with excellent cyclability and large cell voltage (using a EMI-TFSI as the electrolyte). These optimized Si-NTrs were successfully grown on microstructured interdigitated electrodes, paving the way to future integrated all-silicon “on chip” micro-EDLC. Moreover, solid state micro-EDLC were obtained combining silicon nanotrees and ionogel electrolyte, thus leading to highly stable, solder reflow resistant devices able to withstand exceptional temperature conditions with a quasi-ideal capacitive behavior. Finally, the electrode/electrolyte interface was drastically improved by highly conformal surface coatings, leading to extremely large electrochemical windows over 4 V, improved Coulombic efficiency and unprecedented cycling ability over tens of millions of charge/discharge without significant damages. (1) Simon, P.; Gogotsi, Y. Nat. Mater. 2008, (11), 845-54 (2) Beidaghi, M.; Gogotsi, Y. Energy & Environ. Sci. 2014, 7 (3), 867-884 (3) Thissandier, F. et al., Nano Energy 2014, 5, 20-27 (4) Thissandier, F. et al., J. of Power Sources 2014, 269, 740-746 (5) Berton, N. et al., Electrochem. Commun. 2014, 41, 31-34

Electrodeposited copper foams as substrates for thin film silicon electrodes

Although a significant amount of effort has been put into investigating elemental silicon as a lithium-ion battery anode material, limited progress has occurred in translating these results to create a long lived electrode. Several electrode level solutions have been reported including utilizing Si nanowires, thin films, and nanoparticle assemblies, where the physical diffusion distances are kept very short. For thin film based electrodes, the benefits of the simplified structure of the electrode are countered by the low surface area and low silicon loadings. In this study we have utilized electrodeposition techniques to deposit silicon films on a porous copper substrate. This greatly increases the electrode surface area and loadings while maintaining the advantages of a thin film electrode. Using 3d-silicon electrodes without a binder or conductive matrix, stable capacities of ~1000mAh/g have been achieved. In general, electrodes with lower loadings of active silicon (<1mg/cm2) displayed better rate capability than electrodes with higher loadings (>2.5mg/cm2).

Sol-gel preparation of low oxygen content, high surface area silicon nitride and imidonitride materials.

Reactions of Si(NHMe)4 with ammonia are effectively catalysed by small ammonium triflate concentrations, and can be used to produce free-standing silicon imide gels. Firing at various temperatures produces amorphous or partially crystallised silicon imidonitride/nitride samples with high surface areas and low oxygen contents. The crystalline phase is entirely α-Si3N4 and structural similarities are observed between the amorphous and crystallised materials.

멤리스터-CMOS 기반의 잉여 이진 가산기 설계

본 논문은 멤리스터-CMOS 기반의 잉여 이진 부호화 자리수 (RBSD) 가산기를 제안한다. 기존의 RBSD 가산기는 리플 캐리 가산기에 비해 큰 면적을 차지한다. 또한 처리하는 비트 수가 적을 때 연산 속도가 느린 단점이 있다. 제안된 RBSD 가산기는 기존 RBSD 가산기의 단점을 보완하기 위해 멤리스터-CMOS 회로를 사용한다. 제안된 멤리스터-CMOS 기반의 RBSD 가산기는 기존 RBSD 가산기에 비해 단위 셀 면적이 45% 감소하였고, 지연시간이 24% 감소하였다. 제안된 멤리스터-CMOS 기반의 RBSD 가산기의 구현으로 인해 RBSD 가산기의 장점이 더욱 부각되고, 대용량 회로에서 더 큰 이득을 얻는다.

Effects of structural properties of silicon carbide-derived carbons on their electrochemical double-layer capacitance in aqueous and organic electrolytes

High surface area silicon carbide-derived carbons (Si-CDCs) synthesized by chlorination of beta silicon carbide (βSiC) with two different particle sizes (6 μm and 50 nm) show different porosities with graphitic structure. Transmission electron microscopy, Raman spectroscopy and argon (Ar) and carbon dioxide (CO2) sorption analyses are used to examine the textural properties of the Si-CDCs. The results show that the particle size of the precursor affects the surface area and porosity of carbons. Furthermore, an additional heat treatment of the Si-CDC with 50-nm particle size for 24 h at 1,000 °C results in a collapse of the pore structure and reduces the surface area. The capacitive behaviours are investigated in H2SO4 and in tetraethyl ammonium tetrafluoroborate (TEABF4)/acetonitrile (AN). The electrochemical performance of the Si-CDCs is influenced by the particle size, surface area, pore volume and pore size distribution. The Si-CDCs exhibit capacitances in 1 M H2SO4 of up to 179 F g−1 and very stable charge–discharge performance over 5,000 cycles. This study shows the crucial importance of ultramicropores less than 1 nm combined with nanosized particles for achieving high capacitance in aqueous electrolyte. Moreover, the graphitic degree at the surface of the Si-CDCs enhances considerably the rate capability and stability in both electrolytes.

A simple facile approach to large scale synthesis of high specific surface area silicon nanoparticles

An inexpensive, facile, and high throughput synthesis of silicon nanoparticles was achieved by the mechano-chemical reduction reaction of magnesium silicide (Mg2Si) and silicon monoxide (SiO) using a high energy mechanical milling (HEMM) technique followed by acid leaching. Characterization of the resultant product using X-Ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and surface area analyses was performed at various stages of the synthesis process. XRD patterns show that the final product formed is single phase silicon and the nanocrystalline nature was confirmed by the shifted transverse optical (TO) band, characteristic of nc-Si determined by Raman analysis. SEM and TEM shows the presence of particles of different sizes in the range of few nanometers to agglomerates of few microns which is consistent with products obtained from mechanical milling. BET measurements show a very high specific surface area (SSA) of ~190m2/g obtained due to acid leaching which is also validated by the porous nature of the particles confirmed by the SEM images.

CMS Silicon Strip Tracker Monitoring

The CMS Silicon Strip Tracker is the largest detector of its kind ever operated, with a silicon surface area of about 200 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The Silicon Strip Tracker is the sub-detector with the highest number of detector modules within the CMS experiment. Given the complexity of the device, a variety of tools were developed and are used to determine the status of the detector in real time and allow for data qualification and corrective actions when needed. In this paper we describe the monitoring techniques that are used to safely operate the detector and assess the state of its calibration.

ChemInform Abstract: Synthesis, Stability, and Catalytic Properties of High Surface Area Silicon Oxynitride and Silicon Carbide

Abstract The aim of this work is to extend the range of inorganic materials which find application in heterogeneous catalysis, as catalysts or catalyst supports, through use of progress in the field of advanced ceramics. Developments in synthetic routes to high surface area non-oxides (nitrides, carbides, borides) are briefly reviewed. Work on the synthesis, stability and catalytic properties of high surface area silicon oxynitride and silicon carbide is described. For the former compound, three synthetic routes were investigated: the reaction of an amorphous silica with ammonia proved to be the preferred route, giving a silicon oxynitride of ca. 150 m 2 g −1 . The surface composition of the material obtained by the latter method showed good stability, as indicated by retention of surface nitrogen under reducing or oxidising conditions at about 700°C. The oxynitride surface was unreactive towards butene-1, causing no double-bond isomerisation at 400°C. However, the material was also found to be capable of functioning as a solid basic catalyst, catalysing Knoevenagel condensations in solution at 50°C. The use of nitrides as solid basic catalysts appears to be novel, and this result suggests new applications for such materials. In the case of silicon carbide, a mesoporous form was obtained by polymer pyrolysis. The texture shows improved thermal (but not hydrothermal) stability compared to silica. The surface is less reactive than that of the oxynitride, catalysing neither the double-bond isomerisation of butene-1 nor the Knoevenagel condensation. This compound, and the oxynitride, may be useful as inert support materials for reactions involving alkenes.

Silver Coated Platinum Core–Shell Nanostructures on Etched Si Nanowires: Atomic Layer Deposition (ALD) Processing and Application in SERS

A new method to prepare plasmonically active noble metal nanostructures on large surface area silicon nanowires (SiNWs) mediated by atomic layer deposition (ALD) technology has successfully been demonstrated for applications of surface-enhanced Raman spectroscopy (SERS)-based sensing. As host material for the plasmonically active nanostructures we use dense single-crystalline SiNWs with diameters of less than 100 nm as obtained by a wet chemical etching method based on silver nitrate and hydrofluoric acid solutions. The SERS active metal nanoparticles/islands are made from silver (Ag) shells as deposited by autometallography on the core nanoislands made from platinum (Pt) that can easily be deposited by ALD in the form of nanoislands covering the SiNW surfaces in a controlled way. The density of the plasmonically inactive Pt islands as well as the thickness of noble metal Ag shell are two key factors determining the magnitude of the SERS signal enhancement and sensitivity of detection. The optimized Ag coated Pt islands on SiNWs exhibit great potential for ultrasensitive molecular sensing in terms of high SERS signal enhancement ability, good stability and reproducibility. The plasmonic activity of the core-shell Pt//Ag system that will be experimentally realized in this paper as an example was demonstrated in numerical finite element simulations as well as experimentally in Raman measurements of SERS activity of a highly diluted model dye molecule. The morphology and structure of the core-shell Pt//Ag nanoparticles on SiNW surfaces were investigated by scanning- and transmission electron microscopy. Optimized core-shell nanoparticle geometries for maximum Raman signal enhancement is discussed essentially based on the finite element modeling.

Synthesis and characterization of monolithic, high surface area SiO2/C and SiC/C composites

In this study, the synthesis and characterization of high surface area carbon-supported silica and silicon carbide aerogels are presented. An activated carbon aerogel with surface area greater than 3000 m2 g−1 was used as a support for the sol–gel deposition of silica. The resulting silica-coated carbon aerogel retained a surface area greater than 2000 m2 g−1 and showed improved thermal stability in air. The carbon-supported silicon carbide aerogel was made by the carbothermal reduction of the silica-coated carbon aerogel under flowing Ar at 1500 °C. The resulting monolith maintained a surface area greater than 2000 m2 g−1 and was stable to temperatures approaching 600 °C, 100 °C higher than that of the pristine carbon aerogel.

Preparations and Catalytic Applications of High Surface Area Silicon Carbide

We discuss recent developments in the preparation methods of high surface area silicon carbide,such as templated synthesis,sol-gel processing,and polycarbosilane pyrolysis.We provide an overview and an outlook for the applications of high surface area silicon carbide as catalyst support materials.

Converting Stöber Silica and Mediterranean Sand to High Surface Area Silicon by a Reaction under Autogenic Pressure at Elevated Temperatures

We report on a reaction to convert Stöber silica or Mediterranean sand to high surface area silicon (HSAS). The starting silica and/or the sand are reduced by magnesium under the autogenic pressure of the reactants at 750 °C for 5 h. After the MgO is removed, HSAS is formed. The surface areas are 200 and 86 m2/g for the product obtained from the Stöber silica and sand, respectively. The morphology of the final product is almost identical to that of the precursor silica. The products are stable in air because a thin layer of SiO2 is present on the surface of the silicon. We have detected luminescence from the HSAS in the wavelength region of 626−640 nm.